To achieve the effect of a tripod-head-tilt of XX degrees requires the same amount of rise (in mm) for two lenses of the same focal length - regardless of whether the lenses are symmetrical or retro focus.

This can be confirmed by either actual use of the equipment or geometry taking proper account of the effect of retro focus design on the basic optical principals of a lens.

I think you missed my point. True it is the same relative frame movement, but the change apparent camera tilt is not the same.

Lets say that from the photographers position he has to "look up at 45 degrees in order to get a building in the from top to bottom.To achieve the same effect of tilting up the tripod head 45 degrees you would need to shift a lens that is 20mm from the sensor up by 20mm.

A retrofocal lens that is say 40mm from the sensor would have to be shifted up by 40mm to achieve the same apparent tripod head tilt.

I'm sorry, but you are completely wrong..... And for the record, I make a living shifting lense on 98% of my images.

20mm of shift results in the same relative frame movement regardless of the design of the lens. Only focal length and amount of shift matter.

Unless you use some lens tilt or swing.Would you not need to use more shift on a retro focus lens when using tilt or swing to bring the image back within the image circlewhen using a combination of tilt/swing and shift.

I shoot mainly shallow depth of field and use tilt and swing along with shift.

With no tilt or swing I see it's the same...

Main reason whey I would go to my 4x5 rather than the Fuji gx680 if I needed a combination of tilt/swing and shift

Unless you use some lens tilt or swing.Would you not need to use more shift on a retro focus lens when using tilt or swing to bring the image back within the image circlewhen using a combination of tilt/swing and shift.

I shoot mainly shallow depth of field and use tilt and swing along with shift.

With no tilt or swing I see it's the same...

Main reason whey I would go to my 4x5 rather than the Fuji gx680 if I needed a combination of tilt/swing and shift

The further a lens is from the sensor the more the image circle will be skewed by the same amount of tilt. For instance, if you are working with a symmetrical 35mm lens and you tilt it 5 degrees, in order for the center of the image circle to be in center frame, you would need to shift the back tan(5)x35mm, or 3.06mm. If the lens is a 35mm retro focal with a true focal length of say 70mm, to achieve the same thing, you would need to shift the lens tan(5)x70mm, or 6.12mm.

However, this only effects how far away the center of the image circle will be shifted from the center of frame. This will have no effect of how much you will need to shift to get the same view after the centers are lined up. This is because both lenses have the same angle of view, meaning that the same object projected through the lens in both lenses will be the same size in both of the lenses' image circles. If this was not the case, than they would not show the same angle of view.

"Photography is one percent inspiration and ninety-nine percent moving furniture." Arnold NewmanDon't bother just to be better than your contemporaries or predecessors. Try to be better than yourself. William Faulkner

The further a lens is from the sensor the more the image circle will be skewed by the same amount of tilt. For instance, if you are working with a symmetrical 35mm lens and you tilt it 5 degrees, in order for the center of the image circle to be in center frame, you would need to shift the back tan(5)x35mm, or 3.06mm. If the lens is a 35mm retro focal with a true focal length of say 70mm, to achieve the same thing, you would need to shift the lens tan(5)x70mm, or 6.12mm.

However, this only effects how far away the center of the image circle will be shifted from the center of frame. This will have no effect of how much you will need to shift to get the same view after the centers are lined up. This is because both lenses have the same angle of view, meaning that the same object projected through the lens in both lenses will be the same size in both of the lenses' image circles. If this was not the case, than they would not show the same angle of view.

But you are more likely to use up more shift to center the lens and may not have enough left to shift as much as needed for perspective correction with a retro focus.